This invention relates generally to electrical apparatus, and more particularly to a gas insulated transmission line which utilizes a tapered particle-trapping ring for deactivating contamination particles which may be present within the transmission line.
Present compressed gas insulated transmission lines are mostly of a rigid design with a cylindrical aluminum conductor supported on epoxy insulators inside a cylindrical aluminum sheath, the space between the conductor and the sheath being filled with a high dielectric insulating gas such as sulfur hexafluoride at a pressure typical of which is 50 lbs./sq. in. gauge. Used with the insulators are particle traps which provide low field regions which trap and deactivate contamination particles which may be present within the insulating gas. The particle trap ring generally consists of a metallic straight cylinder surrounding the insulator, with slits or perforations at the bottom of the cylinder which ring is in electrical contact with the outer sheath. Particles moving in the applied field move through these slots to be electrically trapped in the very low field region underneath.
Recently, however, a new design of gas insulated transmission line is being investigated which is of a generally more flexible design. This new flexible transmission line typically uses a corrugated aluminum housing to provide increased flexibility for the outer sheath, thereby enabling the transmission line to change directions more readily. However, the use of the corrugated outer sheath has made particle trapping more difficult; the bottom of the corrugations acts as an inefficient particle trap and particles, when they become levitated, usually cross to the conductor to initiate breakdown in the high field region. Further, it is not possible with the corrugated sheath to be able to move particles in the field along the sheath to the particle traps as is done in the present rigid smooth outer sheath systems.
Furthermore, the use of the present cylindrical particle-trapping rings in the flexible design causes additional problems in that it is necessary to take account of the bending of the flexible outer sheath. For example, if the flexible outer sheath were bent along a radius, the trap diameter would of necessity have to be smaller to accommodate the bending so as to maintain the spaced relationship between the particle trapping ring and the outer sheath. This decreased diameter for the straight cylinder particle-trapping ring would result in a lower insulation distance across the insulator, resulting in an increased possiblity of a flashover occurring at a lower voltage across the insulator.